﻿using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;

public partial class ascx_RndNumber : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e) {
            if(!IsPostBack) {
                //  6位数字的验证码
                string str_ValidateCode = GetRandomstr(4);
                //  用于验证的Session
                Session["ImgCode"] = (str_ValidateCode);
                CreateImage(str_ValidateCode);
            }
        }

        #region 生成随机验证码
        public string GetRandomstr(int Num_Length) {
            string Randomstr = string.Empty;
            Random rand = new Random();

            for(int i = 0; i < Num_Length; i++) {
                Randomstr += rand.Next(10).ToString();
            }
            return Randomstr;
        }
        #endregion

        #region 生成随机颜色
        public Color GetRandomColor() {
            //  对于C#的随机数，没什么好说的
            Random RandomNum_First = new Random();
            //  阻止当前线程，以便下一个Random能进行颜色渲染
            System.Threading.Thread.Sleep(RandomNum_First.Next(50));
            Random RandomNum_Sencond = new Random();

            //  为了在白色背景上显示，尽量生成深色
            int int_Red = RandomNum_First.Next(256);
            int int_Green = RandomNum_Sencond.Next(256);
            int int_Blue = (int_Red + int_Green > 400) ? 0 : 400 - int_Red - int_Green;
            int_Blue = (int_Blue > 255) ? 255 : int_Blue;

            return Color.FromArgb(int_Red, int_Green, int_Blue);
        }
        #endregion

        #region 根据验证字符串生成最终带彩色的图象
        public void CreateImage(string str_ValidateCode) {
            //  图片宽度
            int bmpWidth = str_ValidateCode.Length * 9;
            //  图片高度
            int bmpHight = 17;

            Random newRandom = new Random();
            //  图像大小
            Bitmap theBitmap = new Bitmap(bmpWidth, bmpHight);
            Graphics theGraphics = Graphics.FromImage(theBitmap);
            //  白色背景
            theGraphics.Clear(Color.White);

            //  9pt的字体
            Font theFont = new Font("Verdana", 9);

            for(int int_index = 0; int_index < str_ValidateCode.Length; int_index++) {
                string str_char = str_ValidateCode.Substring(int_index, 1);
                Brush newBrush = new SolidBrush(GetRandomColor());
                Point thePos = new Point(int_index * 8, 2);
                theGraphics.DrawString(str_char, theFont, newBrush, thePos);
            }

            //  将生成的图片发回客户端
            MemoryStream ms = new MemoryStream();
            theBitmap.Save(ms, ImageFormat.Png);

            //  需要输出图象信息 要修改HTTP头
            Response.ClearContent();
            Response.ContentType = "image/Png";
            Response.BinaryWrite(ms.ToArray());
            theGraphics.Dispose();
            theBitmap.Dispose();
            Response.End();
        }
        #endregion
    }
